This invention relates to the assembly of cathode-ray tubes, and particularly to an apparatus and method for checking the mask-to-faceplate spacing in a cathode-ray tube during assembly.
Commercial shadow-mask-type picture tubes for color-television receivers include a panel comprising a faceplate having, on its inner surface, a mosaic viewing screen of different color emitting phosphor elements and an electron-gun structure for projecting a plurality of electron beams toward the screen. A curved apertured shadow mask is attached to a frame and mounted in the faceplate panel at a prescribed spacing from the screen. The prescribed spacing is designated q and is defined to be the distance between the screen and the mask measured parallel to the central longitudinal axis of the tube. In the operation of the tube, the electron beam paths are such that each beam impinges upon and excites only one kind of color-emitting phosphor on the screen while being shielded from the other color-emitting phosphor elements by the apertured mask.
In a method for mounting a mask in a color television picture tube, the mask is first attached to a frame to produce a mask-frame assembly. A q-spacer, having a plurality of fixed distance spacing units, is positioned on the inner concave surface of the faceplate. The mask-frame assembly is inserted within the panel over the q-spacer and temporarily mounted on the panel studs by means of leaf springs frictionally engaging hook plates located on the frame. Thereafter, the leaf springs are welded to the hook plates on the frame. In order to check the established q distance, the mask-frame assembly and the spacer insert next are removed and a q-spacing gauge is inserted into the panel. The mask-frame assembly is then reinserted and the q distances are measured. After the q distances are measured, the mask-frame assembly must be removed in order to remove the q-spacing gauge and thereafter reinserted again.
It is desirable to reduce the number of times a mask is inserted and withdrawn from a faceplate panel in order both to reduce damage to the mask that may be caused by handling and to speed the assembly process. The present invention eliminates one of the mask withdrawal and insertion steps by providing novel apparatus and method for checking the mask-to-faceplate q-spacing without the insertion of a gauge between the mask and faceplate.